The nucleotide sequences of the nuclear ribosomal DNA, including ITS1, ITS2 and the 5·8S rDNA, were determined for 54 specimens representing 13 Leveillula species on 50 different host plant species. The maximum nucleotide sequence diversity among taxa in ITS1-5·8S-ITS2 was 7·1%. Phylogenetic analyses revealed that Leveillula species formed six clades and three basal taxa. The taxonomic positions of several species that are well characterized by morphology of conidia, especially primary conidia, are supported by the present molecular analyses. This result shows that the morphology of primary conidia mostly provides a good criterion to identify Leveillula species. Twenty-six collections of Leveillula taurica recovered from 14 different plant families formed a distinct clade with L. chrozophorae, L. duriaei and L. elaeagni, and showed high homology in the ITS regions. Eight isolates of L. taurica recovered from the Asteraceae, Balsaminaceae, Fabaceae and Campanulaceae showed high sequence diversity, in contrast with other L. taurica specimens, and clustered separately or with other taxa. The result of Kishino-Hasegawa and Templeton tests demonstrated that the possibility of monophyly of L. taurica s. lat. could be significantly rejected, indicating that L. taurica s. lat. is a species complex composed of several biological species.